DE102004012819B4 - Power semiconductor component with increased robustness - Google Patents

Abstract

Power semiconductor device with increased robustness, comprising:
A semiconductor body having a first main surface on a front side of the semiconductor body and a second main surface opposite to the first main surface on a rear side of the semiconductor body;
- One on the first main surface (7) arranged first metallization (10), and
A second metallization (12) arranged on the second main surface (11),
- wherein the semiconductor body (1) is electrically contacted with the first metallization (10) on the first main surface (7) and with the second metallization (12) on the second main surface (11),
characterized in that
- Both metallizations (10, 12) as directly on the corresponding main surface (7, 11) of the semiconductor body (1) applied layer having a contact layer (14), which consists of aluminum and has a layer thickness between 1 and 5 nm.

Description

The The present invention relates to a power semiconductor device with elevated Robustness comprising a semiconductor body having a first major surface a front side of the semiconductor body and a second, opposite to the first main surface located main surface on a back the semiconductor body, one on the first main surface arranged first metallization and arranged on the second main surface second metallization.

It has long been the endeavor, the electrical and thermal Resilience of power semiconductor devices, in particular vertical power semiconductor devices to increase. this applies preferably under dynamic loads, such as these, for example during shutdowns, Effects of cosmic radiation, Shorts starting operations or surge currents occur. Namely, in such dynamic loads can be very in power semiconductor devices high current densities occur. This is especially true when form so-called current filaments, which in vertical power semiconductor devices can shift in the lateral direction of the components and with respect to doping or lifetime of the carrier inhomogeneous Positions in the semiconductor body of the power semiconductor component, that is at certain points can dwell the power semiconductor device.

such phenomena, which are caused in particular by Stromfilamente, can to a lead strong local heating of the power semiconductor device and damage this even to its complete destruction. Less critical damage, which are also extremely undesirable, are seen in a permanent increase in leakage currents.

In order to increase the load capacity of power semiconductor components, numerous different measures have already been envisaged: optimization of the edge termination, minimization of the electric field strengths occurring under load in the interior or cell field of the power semiconductor component by suitable doping profiles, improvement of heat dissipation or introduction of the so-called HDR principle (HDR = High Dynamic Robustness; US 6,351,024 ) with increased recombination center density in the edge region.

From the DE 198 40 239 A1 a power semiconductor device is known in which a high-melting-point contact metal, such as titanium (Ti), vanadium (V), niobium (Nb), is used to prevent the melting of a metallization due to radiation-induced electrostatic discharges, especially for metallization on the front side. Tantalum (Ta), molybdenum (Mo) or tungsten (W) is provided. In this case, the metallization may have a multilayer structure in which, for example, a further metal layer of, for example, aluminum (Al) is arranged on a layer of Ti or W provided directly on the front side of the semiconductor body. The layer of high-melting-point contact metal has a layer thickness of between about 100 nm and 3 μm.

Furthermore, from the US 4,692,781 a power semiconductor device is known in which between a metallization and a pn junction, a relatively large distance is maintained to prevent damage by melting the metallization due to electrostatic discharges.

Finally, that describes DE 41 01 274 A1 a power semiconductor device in which after depositing a gate electrode layer of polycrystalline silicon on the structure thus obtained by means of CVD (Chemical Vapor Deposition) stacked a heat-resistant or a high melting point metal layer and a metal silicide layer are applied.

The introduction of the abovementioned measures has resulted in correspondingly designed power semiconductor components being capable of considerably greater dynamic load than power semiconductor components in which these measures are not applied. Despite these measures, however, extreme power densities can still occur in the case of the above-mentioned dynamic processes in the power semiconductor components. These can even become so high that the eutectic temperature of aluminum and silicon is at least temporarily considerably exceeded in the case of a semiconductor body made of silicon. This effect is less critical for the first main surface or front side of the power semiconductor device, since there is little damage caused there because of the relatively short duration of exceeding the eutectic temperature. However, it is of great importance for the second main surface or rear side of the power semiconductor component. In fact, better heat dissipation is usually present on this back side, since the power semiconductor component is applied with its rear side to a carrier. Also, the highest power in the power semiconductor device is dissipated in the region of a near-front pn junction. Therefore, the backside is usually cooler than that Front. This has consequences for the so-called thermomigration:
Experiments have shown that in a semiconductor body thermomigration emanates from the cooler side and spreads to the warmer side of this. In other words, thermomigration occurs around the backside as soon as the temperature exceeds the eutectic temperature of aluminum and silicon.

If, for example, the silicon carbide consists of silicon carbide instead of silicon, the eutectic temperature of a high-melting point contact metal and silicon carbide must naturally be assumed. The same applies to other semiconductor materials, such as A _III B _V compound semiconductors.

The Thermomigration causes when the second metallization on the second main surface made of, for example, aluminum, this aluminum is relatively fast in the semiconductor body can diffuse. This diffusion is the faster, depending steeper is the temperature gradient in the vertical direction of the semiconductor body.

specially in filaments caused by cosmic radiation, Short circuit or extreme switching operations are conditional, can be very steep temperature gradients occur, making the aluminum relatively deep into the semiconductor body can penetrate or migrate. In this migration forms at the end of the respective migration channel in the depth of the semiconductor body, ie For example, in the depth of the silicon wafer, a eutectic Mixture. This eutectic mixture may have the properties of the power semiconductor device significantly affect by specifically significantly increased leakage currents occur. This and also by the p-doping caused by the migration the aluminum atoms along the migration path was generated is the efficiency of the back Emitters changed significantly, and in the worst case Eventually, the power semiconductor device may eventually fail completely or destroyed become.

As remedial measures against the effects of thermomigration, the following could be envisaged:
The back emitter, ie in an IGBT (bipolar transistor with insulated gate) usually the p-type emitter and a diode in general, the n-type Emit ter, as high as possible to dope and deep into the semiconductor body or the semiconductor wafer diffuse , It has been shown that it is precisely the resistance to cosmic radiation of diodes, which have an extremely large penetration depth of the n-type emitter of more than 100 μm, that is great. In general, such a higher shutdown robustness can be achieved by means of a stronger backside emitter. Thanks to this higher shutdown robustness, unwanted stable increases in the leakage current only occur at higher turn-off power levels. A leakage current increase or destruction only occur at higher blocking voltages, that is, they occur when the space charge zone, which spans when the reverse voltage is applied to the two metallizations, penetrates into the rear region of the power semiconductor component. In the case of IGBTs, an amplification of the p-type emitter has a positive effect on the short-circuit behavior, which also applies to a reduction of the temperature gradient in the semiconductor body via a flatter field distribution, as for example in a PT-IGBT (Punch Through).

disadvantageous on all the above remedies but is that in these the emitter trained much stronger is as desired in general is. To the turn-off due to this stronger training of the emitter not to be too high, therefore, must be for a reduction of these shutdown losses be taken care of. This is through a targeted, generally vertical inhomogeneous adjustment of the lifetime of the charge carriers, for example possible by proton irradiation or helium irradiation.

Finally, as another remedial action to be thought against thermomigration, the temperature gradient in the semiconductor body to flatten so that the migration speed of aluminum is reduced. This could be through Use of high purity silicon that contains less isotopes for boosting the thermal conductivity be taken care of in the silicon. The use of such a high purity Materi as is very complex, and the achievable improvement can only be considered marginal become.

One the reverse way is to consciously raise the temperature gradient in the semiconductor body, so that the backside temperature stays below the eutectic temperature. Also this way is to be regarded as unsuccessful, because with him the temperature level is raised overall and, for example, by an increase in the Leakage continues to rise.

From the DE 29 30 779 C2 is a back contact with a first contact metal layer of vanadium, aluminum, titanium, chromium, molybdenum or a nickel-chromium alloy known with a layer thickness of 5 to 200nm. Another back contact shows the US 6,309,965 with a first 30nm thin aluminum layer, which is annealed at 350 ° C before further metallizations are applied.

From the DE 36 32 209 C2 is an electrode structure on a SiC single crystal semiconductor known for which a first metal layer of titanium, chromium or molybdenum with a thickness of 20 to 80 nm is vapor-deposited. In addition, it is known that prior to the application of the first metal layer on the SiC semiconductor surface irregularities or a roughening can be generated by irradiation with ions. GEIB, KM et al .: "Reaction between SiC and W, Mo, and Ta at elevated temperatures", in: J. Appl. Phys., September 15, 1990, pages 2796 to 2800, forms ohmic contacts to SiC by depositing a 30nm thin film of Mo or Ta or a 50nm thin film of W.

The US 5,442,200 forms low-resistance electrical contacts to a SiC semiconductor by means of an unexplained back contact and a front contact according to the invention, which consists of thin films of metal silicides, which have layer thicknesses in the range of about 20nm, for which first a sacrificial silicon layer and then a metal layer is formed and both annealed , From Waldrop, JR et al: "Schottky barrier height and interface chemistry of annealed metal contacts to alpha 6H-SiC Crystal face dependence", Appl. Phys. Lett. 62 (21), 24 May 1993, pages 2685 to 2687 , it is known to form a metal contact on SiC by Ni, Ti or Al, to which about 2.5 to 5 nm of the metal are vapor-deposited samples were investigated with and without subsequent heat treatment, the back contact being made here by an indium-attached molybdenum plate.

It is known from US 2003/002174 A1 for a metallization on the front and back of a GaAs device to produce thin adhesion layers of titanium in a thickness of 100 nm and less than 50 nm. Also the US Pat. No. 5,156,998 uses titanium thin films of thickness 10 to 100nm for metallization on GaAs.

It is therefore an object of the present invention, a power semiconductor device indicate that local overcurrents due to Aluminum, which is undesirably deep due to electrical loading of the device in the semiconductor body penetrated, for example by thermomigration, are largely suppressed, so the electrical capacity this power semiconductor component is increased.

This object is achieved by a power semiconductor component with the features of claims 1, 2 and 6. The features of the preamble of these claims are known from US 5,442,200 as well as from the above-mentioned Waldrop, IR et al.

The Task is in a power semiconductor device of the beginning mentioned type according to the invention thereby solved, that both metallizations than directly on the corresponding main surface of the Semiconductor body applied layer has a contact layer made of aluminum with a layer thickness between 1.0 and 5 nm. Are in the Contact layer, however, still atoms of the semiconductor material of the semiconductor body, at a silicon body consisting of silicon atoms, ie, silicon atoms, incorporated, Thus, the layer thickness of the contact layer between 1.0 to 10 nm amount.

The The above object is in a power semiconductor device of the above mentioned type according to the invention also solved in that at least those on the second main surface, so the back of the semiconductor body envisaged metallization as applied directly on this second major surface Layer has a contact layer, which consists of a hard-melting Metal exists. The layer thickness of this contact layer can be values between 1.0 and 100 nm.

On the thin one Aluminum layer is - as well as on the layer of refractory metal or metal silicide - a common one Multilayer metallization system applied to the respective Complete metallization. This multi-layer metallization system can be made, for example Titanium nitride, nickel, silver, etc. exist. This application takes place as well as a subsequent one Tempering in usual Wise.

at the power semiconductor component according to the invention So is as a direct contact layer of a metallization on the back and front side of the semiconductor body a thin one Aluminum layer or instead of this aluminum layer as direct Contact layer is a layer of refractory metal or Applied metal silicide. Such heavy melting metals are For example, titanium, tantalum, tungsten, molybdenum, chromium or cobalt or silicides these metals or titanium nitride or tantalum nitride. Possibly can while still be installed diffusion barriers.

at the power semiconductor component according to the invention So comes the surface of the semiconductor body on the front and / or back not in direct contact with a mainly aluminum existing subsequently applied metallization.

The thickness of the thin aluminum layer should be so small that no sufficiently large Al / Si drop, which can penetrate into the depth of the semiconductor body, forms. Suitable layer thicknesses are between 1 and 5 nm. At layer thicknesses below 2 nm, cooling of the semiconductor body during the deposition of this layer should be provided to increase the surface mobility of the semiconductor body To reduce aluminum atoms on the surface of the semiconductor body, so that a critical average mass occupancy, above which the thin aluminum layer from a grain structure merges into a continuous layer, is reduced.

A advantageous development of the invention is that the on the surface of the semiconductor body isolated thin Aluminum layer is patterned before the multi-layer metallization is applied with diffusion barriers. This can cause migration effects be further minimized, because the structuring of the aluminum layer limits the amount of for a migration is available standing aluminum: there will be a lateral flow of Aluminum prevents and thus the total amount of the for the migration process to disposal limited aluminum. The lateral extent and the optimal distance of the After structuring, remaining aluminum islands are present all from the thickness of the aluminum layer.

In the thin one Aluminum layer can also be incorporated to the silicon Penetration of the aluminum in the existing semiconductor body of silicon hinder. This measure allows the thickness of the deposited on the surface of the semiconductor body To increase aluminum layer namely, for example, 1.0 to 10 nm. The additions of silicon in an aluminum layer in a semiconductor body made of silicon should approximately in the range between 1 wt .-% and 4 wt .-% of aluminum.

The Power semiconductor device according to the invention is preferably a diode or an IGBT. It can work out though also act to a MOS transistor or a thyristor. specially in a thyristor having an "amplifying gate" structure is the application of the invention particularly advantageous, since here the inner "amplifying gates" when switching with a high current gradient di / dt (i = current, t = time) are loaded with very high current densities and in contrast to the cathode surface no over a pressure contact are cooled on the cathode side. It is then possibly sufficient, the measures specified in the invention only in an interior area, ie in the area of the "amplifying gate" structure to use, since the highest temperatures occur here when switching.

All In general, it can also with other power semiconductor devices be sufficient if the inventive measures only in the areas come to the application, in which in the operation of the power semiconductor device particularly high temperatures occur, such as with diodes, in which the HDR principle is not provided, in the edge area, where at the shutdown the highest dynamic load occurs.

at the power semiconductor component according to the invention is thus in particular on the hitherto customary backside metallization thick aluminum dispensed to the penetration of aluminum in the Semiconductor body in particular to avoid the effect of thermomigration; especially the application of this measure is recommended, if the area under the surface, on which the metallization is deposited, is amorphized since this amorphization facilitates the penetration of aluminum. Instead of of thick aluminum becomes a layer of a hard-melting Metal or a thin one Aluminum layer with a thickness between preferably 1 and 5 nm applied, and subsequently Then, the layer of the refractory metal or the thin one Aluminum layer with the usual Reinforced multi-layer metallization. A thin aluminum layer can additionally be structured so that the amount of penetrating into the surface of the semiconductor body Aluminum atoms is reduced. Also, in the aluminum layer still semiconductor material - in particular Silicon - with be incorporated up to 4 wt .-%.

following The invention will be explained in more detail with reference to the drawings. Show it:

1 a sectional view of an IGBT, wherein two different variants of the power semiconductor component are shown to the left and right of a center line indicated in semicolons, and

2 a plan view of a structured thin aluminum layer.

1 shows a section through an IGBT with a semiconductor body or chip 1 preferably silicon or other suitable semiconductor material, such as silicon carbide (SiC) or A _III B _V compound semiconductors, in particular gallium arsenide. In this semiconductor body 1 is in an n ^- conducting base zone 2 a p-type base zone 3 introduced, in which an n- or n ⁺ -conducting source or emitter zone 4 located. Furthermore, the semiconductor body 1 an n- or n ⁺ -conducting field stop zone 5 and a p-type collector zone 6 on. Of course, the specified cable types can also be reversed.

Become only the zones 3 (P-type), 2 (n ^- -conducting) and if necessary 5 Provided (n-type), so there is a diode. So here are the emitter zone 4 and the collector zone 6 omitted. The following considerations for an IGBT apply in the same way for a diode having such or similar structure.

On a first main surface 7 of the semiconductor body 1 there is an insulating layer 8th from, for example, silicon dioxide and / or silicon nitride. In this insulating layer 8th is a gate electrode 9 made of particular polycrystalline silicon introduced. Of course, a diode does not have such a gate electrode.

In the first main surface 7 are the emitter zone 4 and the p-base zone 3 via a first contact (emitter contact) in the form of a first metallization 10 contacted.

One to the first main surface 7 opposite second major surface 11 of the semiconductor body 1 is with a second contact (collector contact) in the form of a second metallization twelve Mistake.

All generally can in the case of a power semiconductor component with n contacts, all n contacts, n-1 contacts, etc. and only one contact in the manner according to the invention be formed.

The 1 now shows two different variants for the structuring of the metallization according to the invention twelve ,

In the left half is a thin aluminum layer 14 represented, which has a layer thickness of 1 to 5 nm. In this aluminum layer 14 For example, silicon additives may be incorporated at a level of about 1% to 4% by weight. With built-in silicon additives, the layer thickness can then be up to 10 nm.

The aluminum layer 14 can be continuous over the entire main surface 11 of the semiconductor body 1 extend. But it is also possible, this aluminum layer 14 - As shown - only in a region with particularly high temperatures, for example, in the interior, to provide the power semiconductor device.

In the right half of the 1 is instead of the aluminum layer 14 a layer 13 made of a refractory metal or metal silicide. Suitable materials for the refractory metal are, for example, titanium, tantalum, tungsten, molybdenum, chromium or cobalt. Such a layer 13 is preferably on an amorphized or at least partially amorphized surface of the semiconductor body 1 deposited.

In contrast to the aluminum layer 14 can the layer 13 made of heavy melting metal have a greater layer thickness of, for example, 1.0 to 100 nm.

The layer 13 Made of heavy melting metal can be - like the aluminum layer 14 - over the entire main surface 11 extend. However, it can also be provided only in those areas in which particularly high temperatures are to be expected, for example at the edge of the power semiconductor component.

In both variants of the left and the right half of the 1 are on the aluminum layer 14 or on the layer 13 made of heavy melting metal, in each case a Mehrschichtmetallisierungssystem 15 applied. This multi-layer metallization system 15 can in conventional manner, for example, a titanium nitride layer 16 , a nickel layer 17 and a silver layer 18 consist. Other materials are for this multi-layer metallization system 15 possible.

2 shows still a possibility of variation for the design of the aluminum layer 14 in a plan view: this aluminum layer 14 can be from individual areas 14 ' which are island-shaped on the surface 11 of the semiconductor body 1 are applied. By such a structuring is achieved that a lateral Nachfließen of aluminum is prevented. The size of the aluminum islands thus formed and the distance between the individual aluminum islands 14 ' depend on the thickness of the aluminum layer 14 from.

1

Semiconductor body

2

n ^- -type base zone

3

P-type base zone

4

emitter region

5

Field stop zone

6

collector region

7

first main surface

8th

insulating

9

gate electrode

10

first metallization

11

second main surface

12

second metallization

13

layer made of heavy melting metal

14

aluminum layer

14 '

structured aluminum layer

15

Mehrschichtmetallisierungssystem

16

titanium nitride

17

nickel layer

18

silver layer

Claims (12)

Power semiconductor device with increased robustness, comprising: - a semiconductor body ( 1 ) with a first main o surface ( 7 ) on a front side of the semiconductor body ( 1 ) and a second, opposite to the first main surface ( 7 ) ( 11 ) on a back side of the semiconductor body ( 1 ), - one on the first main surface ( 7 ) arranged first metallization ( 10 ), and - one on the second main surface ( 11 ) arranged second metallization ( twelve ), - wherein the semiconductor body ( 1 ) with the first metallization ( 10 ) at the first main surface ( 7 ) and with the second metallization ( twelve ) on the second main surface ( 11 ) is electrically contacted, characterized in that - both metallizations ( 10 . twelve ) than directly on the corresponding main surface ( 7 . 11 ) of the semiconductor body ( 1 ) applied layer a contact layer ( 14 ), which consists of aluminum and has a layer thickness between 1 and 5 nm. Power semiconductor device with increased robustness, comprising: - a semiconductor body ( 1 ) with a first main surface ( 7 ) on a front side of the semiconductor body ( 1 ) and a second, opposite to the first main surface ( 7 ) ( 11 ) on a back side of the semiconductor body ( 1 ), - one on the first main surface ( 7 ) arranged first metallization ( 10 ), and - one on the second main surface ( 11 ) arranged second metallization ( twelve ), - wherein the semiconductor body ( 1 ) with the first metallization ( 10 ) at the first main surface ( 7 ) and with the second metallization ( twelve ) on the second main surface ( 11 ) is electrically contacted, characterized in that - at least one of the two metallizations ( 10 . twelve ) than directly on the corresponding main surface ( 7 . 11 ) of the semiconductor body ( 1 ) applied layer a contact layer ( 14 ), which consists of aluminum, in the atoms of the semiconductor material of the semiconductor body ( 1 ) and which has a layer thickness between 1.0 and 10 nm. Power semiconductor component according to claim 2, characterized in that the contact layer ( 14 ) on the back side of the semiconductor body ( 1 ) is provided. Power semiconductor component according to one of claims 1 to 3, characterized in that the contact layer ( 14 ) is structured. Power semiconductor component according to claim 2, characterized in that in the case of a semiconductor body made of silicon ( 1 ) into the aluminum contact layer ( 14 ) up to 4 wt .-% silicon atoms are incorporated. Power semiconductor device with increased robustness, comprising: a semiconductor body ( 1 ) with a first main surface ( 7 ) on a front side of the semiconductor body ( 1 ) and a second, opposite to the first main surface ( 7 ) ( 11 ) on a back side of the semiconductor body ( 1 ), - one on the first main surface ( 7 ) arranged first metallization ( 10 ), and - one on the second main surface ( 11 ) arranged second metallization ( twelve ), - wherein the semiconductor body ( 1 ) with the first metallization ( 10 ) at the first main surface ( 7 ) and with the second metallization ( twelve ) on the second main surface ( 11 ) is electrically contacted, characterized in that on the first and the second main surface ( 7 . 11 ), ie the front side and the rear side of the semiconductor body ( 1 ) provided metallizations ( twelve ) each as directly on this first or second main surface ( 7 . 11 ) applied layer a contact layer ( 13 ), which consists of a refractory metal and has a layer thickness of 1.0 to 100 nm. Power semiconductor component according to claim 6, characterized characterized in that the heavy-melting metal titanium, tantalum, Tungsten, molybdenum, Chromium or cobalt or a silicide of these metals or titanium nitride or tantalum nitride. Power semiconductor component according to one of claims 1 to 7, characterized in that on the contact layer ( 14 . 13 ) a per se known multilayer metallization system ( 15 ) is applied. Power semiconductor component according to claim 8, characterized characterized in that the multi-layer metallization system is titanium nitride (TiN), nickel (Ni) and silver (Ag). Power semiconductor component according to claim 8 or 9, characterized in that in the multi-layer metallization ( 15 ) Aluminum is installed. Power semiconductor component according to one of claims 1 to 10, characterized in that the contact layer ( 14 . 13 ) only in an edge region or in an inner region of the corresponding main surface ( 11 ) of the semiconductor body ( 1 ) is provided. Power semiconductor component according to one of claims 6 to 11, characterized in that the area under the main surface on which the contact layer ( 13 ) is deposited, amorphized or at least partially amorphized.